HI, I'm trying to create a simple database for my C# .NET application. It's easy enough to create a db and to run it locally, but I was wondering which is the best free one I should Use? Furthermore, I would also like the application to be easily deployable on multiple PCs (each with their own local db instance). What is the best tool for me to use?

+1 SQLite can be 'deployed' with your assembly by including the dll in the output directory. It also is fairly fast and lightweight (compared to something like SQL Server Compact). It is probably the most tested free portable database.
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wllmsaccntFeb 1 '11 at 19:19

IMO, SQL Server Express is overkill for a single user on a single machine. It takes up precious memory, is always running in the background, and it also complicates the installation. SQL CE is a better choice me thinks...
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BFreeFeb 1 '11 at 19:40

Note that may users are suggesting SQL Server Compact Edition. It could be useful to know the difference. CE is much more limited, but easier to deploy. Sounds like CE is the better choice for your application.